and the Mode of it's Communication. 173 
for the compensation it receives for this loss, from the disk B. 
This disk, being hotter than the thermoscope, gives to it con- 
tinually, more radiant caloric than it receives from it; and, 
were it not for the simultaneous loss of caloric which the instru- 
ment sustains, in its interchanges with the cold disk A, its 
quantity of caloric would be augmented, and it would become 
hotter. 
Now, as the temperature of the ball of the thermoscope is an 
arithmetical mean between that of the disk A and that of the 
disk B, it is reasonable to suppose, that the thermoscope receives 
just as much fnofe caloric from B than it gives to it, as it gives 
to A more than it deceives from it; and, if that be the case in 
fact, it is evident, that the simultaneous actions of the two disks 
on the ball of the therfnoscope (or the traffic which they carry 
on With it in caloric) can neither tend to increase, nor to di- 
minish, the original stock of that substance belonging to that 
instrument ; consequently, the instrument will neither be heated, 
nor cooled, by these interchanges, but will continue invariably 
at the same constant temperature. 
This explanation is plausible ; but, before the hypothesis on 
which it is founded can be admitted, we must see if it will agree 
with the results of other experiments ; for the greatest care 
ought always to be used in the admission of hypotheses in phy- 
sical researches ; and, in no case can it be more indispensably 
necessary, than where an hypothesis has evidently been con- 
trived for the sole purpose of explaining a single experiment, or 
elucidating a new fact. 
When the surface of the metallic disk B was blackened, by 
holding it over the flame of a candle, the intensity of its radiation , 
